Caveolin-1 interacts and cooperates with the transforming growth factor-β type I receptor ALK1 in endothelial caveolae

Aims: Activin receptor-like kinase (ALK)1 is a transforming growth factor (TGF)-β type I membrane receptor restricted almost entirely to endothelial cells (ECs) and involved in vascular remodelling and angiogenesis. Previous reports have shown that the ubiquitous TGF-β type I receptor ALK5 and the type II receptor are located in cholesterol-rich membrane microdomains named caveolae. The aim of this work was to assess the location of ALK1 in endothelial caveolae as well as to study the role of caveolin-1 on the TGF-β/ALK1 signalling pathway. Methods and results: The subcellular distribution of ALK1 was analysed by confocal microscopy and co-fractionation experiments in human ECs. The association between human ALK1 and caveolin-1 was studied in caveolin-1-deficient human epithelial cells by co-immunoprecipitation. The functional role of caveolin-1 on the ALK1-mediated TGF-β signalling was elucidated using ALK1-specific luciferase reporters in human ECs, caveolin-1-/-mouse embryonic fibr